1. Field of the Invention
The present invention relates to a multilayer ceramic capacitor, and particularly relates to a multilayer ceramic capacitor having a large capacitance, large capacitance even in a compact size, and high reliability.
2. Description of the Related Art
A gain capacitance of a multilayer ceramic capacitor is in a relationship of a formula (1) below.C=ε0·εr×n×S/d  (1)                (C: capacitance (F), ε0: vacuum permittivity, εr: specific permittivity of dielectric material, n: number of layers, S: valid area, d: thickness of dielectric)        
Accordingly, in order to increase capacitance, there are methods of making the dielectric layer thickness d thinner, increasing the specific permittivity εr, increasing the valid area S and increasing the number n of dielectric layers.
However, since there is a limit in increasing the valid area to obtain a large capacitance in a compact size, a method of increasing the permittivity or making the layer thinner is generally used.
Owing to the problem of unevenness of thickness, there has been said that the limit of a thinner dielectric layer was 10 μm or 5 μm, but a product having a thinner layer than the limit has come to be produced due to development of production techniques.
Even if a chip capacitor of an extremely thin layer wherein the dielectric thickness is 3 μm or less can be produced, however, there arises a disadvantage that it cannot stand a practical use because resistance of the dielectric is too low. Therefore, a method of making a dielectric particle diameter between internal electrodes less than the thickness of a dielectric layer and making the number of dielectric particles between the electrodes two or more has been taken in the related art. It is for placing a grain boundary phase and securing insulation resistance by making the number of dielectric particles between electrodes two or more. Note that the state that the number of dielectrics between electrodes is two or more means that a straight line drawn vertically from one internal electrode to an internal electrode next to it passes through two or more particles.
However, when the layer becomes still thinner and the dielectric thickness becomes 3 μm or less, it is necessary to make the particle diameter 1.5 μm or less in order to make the dielectric particles between the internal electrodes two or more, so there has been a disadvantage that the gain capacitance cannot be made larger.
Thus, capacitance per volume inevitably becomes small and that has been an obstacle of attaining a compact size and larger capacitance.
Note that, as described in the Japanese Unexamined Patent Publication No. 11-317322, a capacitor wherein a particle diameter of about 20% or more of dielectric particles constituting the dielectric layer of the multilayer ceramic capacitor have a substantially same thickness as that of the dielectric layer has been proposed. This publication discloses improvement of the CR product, which is a product of the capacitance and resistance of the capacitor, by applying such a configuration.
This publication, however, only discloses multilayer ceramic capacitors wherein an average particle diameter of the dielectric particles is same or less than the thickness of the dielectric layer.